The present invention relates to a wheelchair wherein the center of gravity of a person seated on an integral chair is substantially maintained when the chair tilts. The tiltable chair is operatively and slidably mounted on generally any type of frame structure.
Heretofore, chairs per se or wheelchairs have existed wherein the chair back, or the chair back and base (seat), were reclinable.
For example, U.S. Pat. No. 3,758,151 to Re relates to a reclining chair adapted to be positioned in close adjacency to a room wall when in the upright sitting position and yet so structured as to allow ready assumption of any of a variety of reclined positions of occupancy without physical contact of any element thereof with the same room wall, the chair concept envisioning a fixed platform, a chassis movable linearly relative to the platform, and a body-supporting unit movable between the sitting and reclining positions relative to the chassis with a concomitant movement of a leg supporting unit between the retracted and extended positions respectively, a propeller link or other means connecting between the body-supporting unit and platform for propelling the body-supporting unit relative to the platform, with the chassis moving forwardly and progressively away from the wall as transition is made from upright sitting position to progressive positions of reclination, wherefore the body supporting unit is concomitantly moved forwardly away from the room wall, and with the chassis moving rearwardly and progressively toward the wall as transition is made from positions of reclination to upright sitting position, wherefore the body-supporting unit is concomitantly moved rearwardly and toward the room wall.
U.S. Pat. No. 4,759,561 to Janssen relates to a wheelchair comprising an underframe with front and rear wheels, and a seat part (1) which is adjustable relative to the underframe, which seat part (1) can be tilted forward and backward relative to the underframe in such a way that the overall center of gravity (6) of seat part (1) and wheelchair user (5) essentially assumes a fixed position relative to the underframe.
U.S. Pat. No. 4,966,379 to Mulholland relates to a wheelchair having opposing sideframes each of which comprise a base section which is pivotally connected by a brace member to an inclinable seat section. An extender mechanism interconnects the seat section to a brace member and provides releasable securement for a wheelchair seat at selected angular positions. Backrest bars are independently adjustable with a similar extender mechanism that interconnects the bars with a respective seat section. The sideframes are spaced apart with hinged spacer bars, which includes a latching device for releasably securing the bars in an open position. The bar and frame sections have elongated slots containing fasteners for adjustable connections with fasteners from adjunct wheelchair assemblies.
U.S. Pat. No. 5,044,647 to Patterson relates to a kit or assembly which can be used in the manufacture of a new wheelchair or to retrofit an existing wheelchair. The basic wheelchair structure includes a base portion having a pair of cross members mounted in the rear half of the upper portion of the wheelchair base structure. A pair of parallel guide rails is mounted between the cross members with a seat support bar attached to a pair of pillow blocks mounted on the guide rails. A linear actuator is centrally positioned within the wheelchair base structure to longitudinally move the seat support bar forwardly or rearwardly within the wheelbase of the wheelchair. A rear edge of a wheelchair seat unit is pivotally attached to the upper surface of the seat support bar. Cam plates, each having a curved cam slot, are provided on each side of the seat unit with the cam slots engaging cam followers mounted on a pair of stanchions provided on each side of the rear portion of the base structure. A control switch causes the linear actuator to move the seat support bar in a forward or rearward direction, which causes the seat unit to move causing the cam follower pins positioned within the cam slots to tilt or angularly move the seat unit to a maximum reclined position of approximately 60 degrees. The entire seat unit is moved forward a predetermined distance to obtain the desired degree of tilt and to maintain the center of gravity substantially centered within the base structure to maintain the balance and stability of the wheelchair and the safety of the patient.
U.S. Pat. No. 5,297,021 to Koerlin et al. relates to a wheelchair seat having a backrest assembly with a counter balance to provide equilibrium. A control loop is included on the sliding backrest to sense the onset of shear and compensate the backrest to a zero shear position during recline. A leg rest assembly has a selectable lift arrangement for either independent or recline lift.
The present invention relates to a tiltable chair having a constant center of gravity tilt assembly. The chair contains a pivot point at generally the junction of the chair seat and chair back which junction is connected to the tilt assembly comprising a longitudinal guide member slidable along a substantially horizontal and linear guide rail. An actuator, which causes the chair to move either forward or backward, is operatively connected to the wheelchair frame structure and to the slidable guide member. As the chair moves forward, a link arm, which is operatively connected to the frame structure at one end and to a chair seat pivot point at the other end, causes the chair to rotate or tilt backward. Desirably, the link arm is approximately the same length as the distance from the seat pivot point to the chair pivot point. The rearward tilt of the center of gravity of a person seated in the chair is such that it is substantially equal to the forward movement of the chair so that said center of gravity of a seated person is substantially maintained. The chair can be tilted either manually or by the utilization of an actuator.